The biological cell is an extremely advanced microscopic entity that can look after itself, but it's not exactly what you'd call smart. That's all about to change, though, because scientists are now making cells that can perform arithmetic—and the next stop stop is a living implant that can act as a computer.

Scientists at the Swiss Federal Institute of Technology in Zurich have created biological versions of digital circuits inside two sets of embryonic kidney cells. One is a half adder, the other a half subtractor—in other words, they're circuits capable of adding or subtracting binary numbers.

In fact, they're the most complex biological circuits yet created, and the idea is that they could be put to use in computational devices for the body to diagnose diseases, administer drugs or even interface with other electronic devices. The development is published in Nature.

Computers usually use 1s and 0s to perform calculations. In these new cellular circuits, those bits are replaced with two naturally occurring molecules—erythromycin and phloretin—which act as inputs to switch reactions in the cells on or off. The reactions cause red or green fluorescent proteins to be produced, in turn signalling the result of the calculation.

What's most amazing is that the reactions—and hence calculations—take place without interfering with the biologic function of the cells, so they can happily live and function properly inside the human body.

The only problem—and there's always a problem with this kind of research—is that the output of the cells currently can't be used as the input to another, because the answer is given as a color of light, and not in terms of the input molecules. Still, if the team can work around that, it immediately opens up the possibility of using the cells to build up complex computational devices—and from there, a cellular computer is a cinch. [Nature via New Scientist]